THIS invention relates to hydraulically powered mechanisms.
The specifications of South African patents 92/4302 (Trade Firm 57 (Pty) Limited) and 96/7417 (White Manufacturing (Pty) Limited), the contents of both of which are incorporated herein by reference, describe hydraulically powered rotary indexing mechanisms for rotationally indexing the drill steel of a water-powered rockdrill. In each case differential hydraulic forces acting on opposed piston assemblies are used to achieve rotary oscillation of a rotor which transmits indexed rotary motion to the drill steel via a one-way clutch and chuck in which the drill steel is engaged.
The piston assembly in each case includes a strut or plunger which has a spherically shaped end seating in a complemental socket in a radially projecting lug or ear on the rotor. A problem inherent in each of these known mechanisms is the fact that the spherical interface between the plunger or strut and the rotor socket is an area of high wear.
According to one aspect of the invention there is provided an hydraulically powered mechanism comprising a piston assembly arranged to be driven by hydraulic fluid acting on it in a working zone, an item of equipment which is to be driven by the piston assembly, the piston assembly presenting a face which acts at an interface against a complemental face on the item of equipment, and a fluid supply passage for supplying hydraulic fluid from the working zone to the interface.
The piston assembly may include a piston and a strut which acts between the piston and the item of equipment with a portion of the passage extending through the strut to the interface. The interface may be a spherically curved interface between a spherically curved end of the strut and a spherically curved socket in the item of equipment, and the spherically curved end of the strut can be formed with a flat. The piston itself may be cup-shaped to receive an end of the strut remote from the interface, a portion of the passage extending through the base of the piston, from the working zone, to communicate with that portion of the passage extending through the strut.
There may be piston assemblies acting at spaced apart interfaces on the item of equipment and a port extending through the item of equipment to provide hydraulic communication between the interfaces. This would typically be the case where the mechanism forms part of a rotary indexing mechanism of an hydraulically powered rockdrill which serves to rotate a drill steel with indexed rotation. In this case, the item of equipment will be a rotor with the complemental face provided by a radial lug of the rotor.
In an hydraulically powered rockdrill, another aspect of the invention provides a rotary indexing mechanism for rotationally indexing a drill steel attached to the rockdrill, the mechanism comprising:
a rotor,
opposed piston assemblies arranged to be driven by hydraulic fluid acting on them, the piston assemblies presenting faces which act at respective interfaces against complemental faces on the rotor thereby to drive the rotor in rotary oscillation.
means to convert rotary oscillation of the rotor into indexed rotation of the drill steel, and
one or more fluid supply passages for supplying hydraulic fluid to the interfaces.
Typically in this application the piston assemblies are arranged to be driven by hydraulic fluid acting on them in respective working zones, the mechanism comprising one or more fluid supply passages for supplying hydraulic fluid to the interfaces from at least one of the working zones. Typically also, each interface is a spherically curved interface between a spherically curved end of a strut and a spherically curved socket in the rotor lug. The spherically curved end of each strut may be formed with a flat and there may be a port extending through the lug to provide hydraulic communication between the interfaces, the flats serving to ensure that such communication is maintained even if the struts rotate somewhat relative to the lug.